Multiple-step epitaxial growth S/D regions for NMOS FinFET

Abstract

A method of forming NFET S/D structures with multiple layers, with consecutive epi-SiP layers being doped at increasing dosages of P and the resulting device are provided. Embodiments include forming multiple epi-Si layers in each S/D cavity of a NFET; and performing in-situ doping of P for each epi-Si layer, wherein consecutive epi-Si layers are doped at increasing dosages of P.

What is claimed is: 
     
       1. A method comprising:
 forming multiple epitaxially grown (epi) silicon (Si) layers in each source/drain (S/D) cavity of a n-type field effect transistor (NFET); 
 performing in-situ doping of phosphorous (P) for each epi-Si layer, wherein consecutive epi-Si layers are doped at increasing dosages of P,
 wherein two epi-Si layers are formed, each layer formed to a thickness of approximately one-half of a depth of each S/D cavity. 
 
 
     
     
       2. The method according to  claim 1 , comprising performing each of the P doping at a dosage of 1e18 per centimeter cubed (cm 3 ) to 1e21/cm 3 . 
     
     
       3. The method according to  claim 1 , further comprising:
 forming an additional epi-Si layer in each S/D cavity prior to each epi-Si layer or between each pair of epi-Si layers and performing in-situ doping of carbon (C) for each additional epi-Si layer. 
 
     
     
       4. The method according to  claim 3 , comprising forming two or three epi-Si layers and two additional epi-Si layers. 
     
     
       5. The method according to  claim 3 , comprising forming each additional epi-Si layer to a thickness of about one half of a thickness of each epi-Si layer. 
     
     
       6. The method according to  claim 3 , comprising forming each additional epi-Si layer to a thickness greater than or equal to 1 nanometer (nm) and less than a thickness of each epi-Si layer. 
     
     
       7. The method according to  claim 3 , comprising performing each C doping and each P doping at a dosage of 1e18 per centimeter cubed (cm 3 ) to 1e21/cm 3 . 
     
     
       8. A method comprising:
 forming three epitaxially grown (epi) silicon (Si) (epi-Si) layers in each source/drain (S/D) cavity of a n-type field effect transistor (NFET), each epi-Si layer formed to a thickness of approximately one-third of a depth of each S/D cavity; and 
 performing in-situ doping of phosphorous (P) for each epi-Si layer, wherein consecutive epi-Si layers are doped at increasing dosages of P between 1e18 per centimeter cubed (cm 3 ) to 1e21/cm 3 . 
 
     
     
       9. The method according to  claim 8 , further comprising:
 forming two additional epi-Si layers in each S/D cavity, each additional layer formed between a pair of adjacent epi-layers and formed to a thickness of about one half of a thickness of each epi-Si layer; and 
 performing in-situ doping of carbon (C) at a dosage of 1e18 per centimeter cubed (cm 3 ) to 1e21/cm 3  for each additional epi-Si layer.